From 89cd48fcac6c8b11a1a1cb155d3ddf6747719e7c Mon Sep 17 00:00:00 2001
From: Andy Wingo <wingo@pobox.com>
Date: Sun, 19 Dec 2021 11:06:36 +0100
Subject: [PATCH] Implement scm_logbit_p with new integer library

* libguile/integers.c (scm_integer_logbit_ui, scm_integer_logbit_uz):
* libguile/integers.h: Declare the new internal functions.
* libguile/numbers.c (scm_logbit_p): Use new internal functions.
---
 libguile/integers.c | 20 ++++++++++++++++++++
 libguile/integers.h |  3 +++
 libguile/numbers.c  | 18 ++----------------
 3 files changed, 25 insertions(+), 16 deletions(-)

diff --git a/libguile/integers.c b/libguile/integers.c
index ff5499af9..fc71c7acc 100644
--- a/libguile/integers.c
+++ b/libguile/integers.c
@@ -2008,3 +2008,23 @@ scm_integer_logtest_zz (SCM x, SCM y)
 {
   return scm_is_eq (scm_integer_logand_zz (x, y), SCM_INUM0);
 }
+
+int
+scm_integer_logbit_ui (unsigned long index, scm_t_inum n)
+{
+  if (index < SCM_LONG_BIT)
+    /* Assume two's complement representation.  */
+    return (n >> index) & 1;
+  else
+    return n < 0;
+}
+
+int
+scm_integer_logbit_uz (unsigned long index, SCM n)
+{
+  mpz_t zn;
+  alias_bignum_to_mpz (scm_bignum (n), zn);
+  int val = mpz_tstbit (zn, index);
+  scm_remember_upto_here_1 (n);
+  return val;
+}
diff --git a/libguile/integers.h b/libguile/integers.h
index 56334f0a8..feba5963f 100644
--- a/libguile/integers.h
+++ b/libguile/integers.h
@@ -148,6 +148,9 @@ SCM_INTERNAL int scm_integer_logtest_ii (scm_t_inum x, scm_t_inum y);
 SCM_INTERNAL int scm_integer_logtest_zi (SCM x, scm_t_inum y);
 SCM_INTERNAL int scm_integer_logtest_zz (SCM x, SCM y);
 
+SCM_INTERNAL int scm_integer_logbit_ui (unsigned long bit, scm_t_inum n);
+SCM_INTERNAL int scm_integer_logbit_uz (unsigned long bit, SCM n);
+
 
 
 #endif  /* SCM_INTEGERS_H */
diff --git a/libguile/numbers.c b/libguile/numbers.c
index 26d1c061f..548618e74 100644
--- a/libguile/numbers.c
+++ b/libguile/numbers.c
@@ -3155,23 +3155,9 @@ SCM_DEFINE (scm_logbit_p, "logbit?", 2, 0, 0,
   iindex = scm_to_ulong (index);
 
   if (SCM_I_INUMP (j))
-    {
-      if (iindex < SCM_LONG_BIT - 1)
-        /* Arrange for the number to be converted to unsigned before
-           checking the bit, to ensure that we're testing the bit in a
-           two's complement representation (regardless of the native
-           representation.  */
-        return scm_from_bool ((1UL << iindex) & SCM_I_INUM (j));
-      else
-        /* Portably check the sign.  */
-        return scm_from_bool (SCM_I_INUM (j) < 0);
-    }
+    return scm_from_bool (scm_integer_logbit_ui (iindex, SCM_I_INUM (j)));
   else if (SCM_BIGP (j))
-    {
-      int val = mpz_tstbit (SCM_I_BIG_MPZ (j), iindex);
-      scm_remember_upto_here_1 (j);
-      return scm_from_bool (val);
-    }
+    return scm_from_bool (scm_integer_logbit_uz (iindex, j));
   else
     SCM_WRONG_TYPE_ARG (SCM_ARG2, j);
 }